* List the factors that influence the selection of an appropriate
fertility program

* Explain why nitrogen is the key nutrient in a turfgrass fertility
program

* Distinguish between fast-release and slow-release nitrogen
carriers

* Discuss the rate and frequency of fertilizer application for
turfgrass

* Describe methods of fertilizer application

Introduction

As explained in Chapter 7, turfgrass plants require seventeen
essential elements to grow and complete their life cycle. These
nutrients are divided into three groups based on the amounts of each
needed by plants (Figure 10-1). Carbon, hydrogen, and oxygen are
obtained from air or water and are readily available to turfgrass. The
other fourteen elements are removed from the soil by plant roots.

The three elements that receive the greatest attention from
turfgrass managers are nitrogen, phosphorus, and potassium because they
are usually added to the soil at regular intervals. They are referred to
as primary nutrients because turfgrass requires larger quantities of
nitrogen, phosphorus, and potassium than it does of the other eleven
elements obtained from the soil. They are also called fertilizer
nutrients because of their presence in most fertilizers. Of the three,
nitrogen is most likely to be deficient in the soil.

Calcium, magnesium, and sulfur are called secondary elements.
Calcium and magnesium are normally supplied to the soil by the
application of liming materials. Sulfur is added to the soil by using
fertilizers that contain the nutrient or acidifying materials for
lowering soil pH such as elemental sulfur and aluminum sulfate. Some
sulfur ends up in the soil because of air pollutants (sulfur dioxide) or
the application of sulfur-containing pesticides.

Micronutrients or trace elements are materials required in very
small amounts by plants. These minor nutrients are found in plants in
quantities measured in parts per million (ppm). However, they are just
as essential to turfgrass growth as the primary nutrients, no matter how
minute the amount required by the plant (Figure 10-2). In many areas of
the United States it is not necessary to apply micronutrients. With the
exception of iron, micronutrient deficiencies are rare.

Fertilizer

Fertilization is the practice by which nutrients are supplied for
plant growth. Most fertilizers are applied in a dry form with a spreader
(Figure 10-3). Nutrients also are mixed with water and sprayed on turf.
This latter practice is commonly performed by many lawn care services
and is also common on putting greens. Most fertilizers contain nitrogen,
phosphorus, and potassium and are called complete fertilizers. If, for
some reason, it is not necessary to apply one of these primary
nutrients, the turf manager may use a fertilizer that contains the other
two. Individual carriers that supply nitrogen, phosphorus, or potassium
alone are also available. In regions where secondary or micronutrients
are deficient in the soil, fertilizers often contain these elements as
well.

[FIGURE 10-3 OMITTED]

The fertilizer analysis states the percentage of nutrients in a
fertilizer. Generally the analysis percentages are rounded down to whole
numbers and called the grade. The fertilizer grade is the minimum
guaranteed analysis of a fertilizer. The three numbers on a bag of
fertilizer represent its grade. The first number in the sequence
indicates the percentage of elemental nitrogen (N), the second is
available phosphoric acid ([P.sub.2][O.sub.5]), and the third is soluble
potash ([K.sub.2]O).

Fertilizer ratio is another important fertilizer term. A 30-10-10
fertilizer contains three parts of nitrogen for each one part of
[P.sub.2][O.sub.5] and [K.sub.2]O. It is said to have a 3:1:1 ratio. The
20-5-10 fertilizer mentioned earlier has a 4:1:2 ratio. Rather than
recommending a specific grade, turfgrass specialists often suggest using
a fertilizer that has a certain ratio. If a 2:1:1 ratio is recommended,
for example, the turf manager may choose a 20-10-10, 10-5-5, 14-7-7, or
18-9-9 fertilizer.

The correct fertilizer ratio depends on the quantity of available
nutrients in the soil. The quantities of phosphorus and potassium that
are available for plant use can be accurately determined by testing the
soil. As discussed in Chapter 8, soil test results enable the turf
manager to develop the most effective and efficient fertility program.
The quantity of essential elements in the soil depends on the amount and
type of fertilizer applied previously, the level of nutrients that occur
naturally in the soil, and the extent of nutrient losses from the soil.

Nutrient Losses

Losses are due to four causes. A large amount of nutrients is
removed from the soil by the plants themselves. If grass clippings are
allowed to remain on the turf, then most of these nutrients are returned
to the soil and can be used by the turfgrass again. However, when the
clippings are collected and removed from the site, the nutrients are no
longer available to the plants. Some nutrients are converted to gaseous
forms and diffuse into the atmosphere. Leaching by water from rain or
irrigation results in nutrients being moved below the reach of turfgrass
roots. A further, temporary loss occurs when nutrients become
"fixed" in the soil. Because of various chemical reactions
they are converted to insoluble, unavailable forms.

Effect of Maintenance on Nutrition Program

The level or degree of turfgrass maintenance has a major effect on
the nutrition program. Low-maintenance, utility sites usually receive
minimal fertilization because quality is relatively unimportant. One
light fertilizer application per year may be sufficient. The turf
manager desires a vigorous, dark green, dense turf on a higher
maintenance site. Better quality turf can only be achieved by supplying
greater amounts of fertilizer.

Figure 10-4
Useful fertilizer conversions.
To convert [P.sub.2][O.sub.5] to P multiply by 0.44
To convert P to [P.sub.2][O.sub.5] multiply by 2.29
To convert K2O to K multiply by 0.83
To convert K to K2O multiply by 1.2

Unsatisfactory turfgrass is often the direct result of insufficient
fertilization. The quality of many turf areas could be improved
dramatically by increasing the fertilization rate and number of
fertilizer applications. Fertilizer is the best investment dollar for
dollar in a successful turf management program.

Nitrogen

Nitrogen is the key nutrient in a turfgrass fertility program. With
the exception of carbon, hydrogen, and oxygen, plants require more
nitrogen than any other essential element. On a dry weight basis, a
healthy turfgrass plant is composed of 3 to 5 percent nitrogen. This
nutrient is more likely to be deficient than the other sixteen essential
elements. There are several reasons for this. Abundant levels of
nitrogen are not normally found in soils. When nitrogen-containing
fertilizer is applied to the soil, significant quantities of this
nutrient may be lost because of leaching and volatilization. As
mentioned in Chapter 7, the nitrate ion (N[O.sub.3.sup.-) is the
chemical form most commonly used by plants. It is very susceptible to
leaching because it has a negative charge and is not stored in the soil
on cation exchange sites. Volatilization is the loss of nitrogen to the
atmosphere in a gaseous form. It is most common on alkaline soils when
the nitrogen is not watered in after application.

Nitrogen losses are especially severe when the turfgrass is growing
on a sandy soil and irrigation occurs frequently. Sandy soils are very
prone to leaching, and heavy irrigation results in a larger amount of
nitrogen being washed down beneath the root zone. Clipping removal also
leads to nitrogen depletion.

Nitrogen has many important functions in a turfgrass plant. It is a
component of chlorophyll, proteins, amino acids, enzymes, and numerous
other plant substances. The effects of nitrogen fertilization are
readily seen. Shortly after the fertilizer is applied the plants turn a
darker green color and vertical shoot growth increases significantly.

Because nitrogen is the key nutrient in turfgrass nutrition,
fertility programs are normally expressed in terms of how many pounds of
nitrogen per 1,000 [ft.sup.2] (kilograms per 93 [m.sup.2]) are applied.
Unfortunately, soil tests are not particularly helpful in determining
nitrogen fertilization rates. (The reasons for this have been discussed
in detail in Chapter 8.) Consequently, unless tissue testing is
performed, turf managers must base their nitrogen fertility program on
visual observations, general recommendations from turfgrass specialists,
and other considerations (Figure 10-5).

The need to apply nitrogen can be determined by quality indicators
such as color and density. The nutrient is an important component of the
chlorophyll molecule, and nitrogen-deficient plants turn a yellowish
green color. This condition is known as chlorosis. When grass becomes
chlorotic and loses its desirable green color, the manager may want to
apply fertilizer. However, before fertilizing, he or she should be
certain that the turf has not turned color because of environmental
stress or pest problems. It is also important to remember that turf does
not have to be dark green to be healthy.

Figure 10-5
Some factors that effect the total amount of nitrogen that
should be applied during the growing season.
Quality indicators--color, density, and uniformity
Soil texture (sands may require more)
Amount of irrigation (irrigation results in more growth and use,
possibly more leaching)
Clippings (returned or removed)
Shade (less sun = less growth = less need for fertilizer)
Grass species and cultivars present
Need for recuperation (sports turf)
Type of fertilizer (fast-release versus slow-release nitrogen)
Disease problems (too much or too little nitrogen favors certain
diseases)
Length of growing season
Leaching concerns (likelihood of water pollution by nitrates)
Green speed (less nitrogen results in increased ball roll distance)
Budget

Density is the most important indicator. A thin, open turf
populated with weeds is often caused by inadequate nitrogen fertility. A
third indicator sometimes used to assess nitrogen levels is clipping
yield. Low levels of available nitrogen result in a slower vertical
growth rate and a reduced mowing frequency.

Nitrogen fertilization, based on these quality indicators, is
greatly influenced by the degree of turf quality that is desired. A
low-maintenance area may receive as little as 1 pound of nitrogen per
1,000 [ft.sup.2] a year, whereas the rate for a highquality bermudagrass
turf may be as much as 12 to 16 pounds of nitrogen per 1,000 [ft.sup.2]
a year. Other factors that affect how much nitrogen is applied include
the soil texture, the amount of irrigation, whether clippings are
removed, the type of nitrogen source used, the length of the growing
season, the species and cultivars that compose the turf, the degree of
shading, and the size of the maintenance budget. A sports turf usually
requires extra nitrogen because the grass must be aggressive. Foliar
analysis (tissue testing) can be used to help establish fertilizer
needs. In most cases turf managers base their nitrogen rates on the
appearance and performance of the turf.

Overfertilization can be just as detrimental as not applying enough
nitrogen. Excessive rates cause physiologic changes in a plant such as
thinner cell walls, more tender, succulent tissue, and reduced food
reserves. These changes result in decreased heat, drought, cold, and
wear tolerance. Disease resistance is also diminished. The application
of too much nitrogen significantly increases the need for mowing because
of the rapid shoot growth it stimulates.

The nitrogen found in most fertilizers is produced by nitrogen in
the atmosphere reacting with natural gas (methane). The result of this
reaction is the formation of ammonia, which is then combined with other
chemicals such as nitric acid, sulfuric acid, phosphoric acid, and
carbon dioxide. The end products of these reactions are four common
nitrogen carriers--ammonium nitrate (33-0-0), ammonium sulfate (20-0-0),
ammonium phosphate (11-48-0, 20-50-0), and urea (45-0-0). The form of
nitrogen in these carriers is 100 percent water soluble and is
immediately available for plant use. These carriers are said to be
quickly available or fast-release sources of nitrogen. Urea is widely
used on turfgrass.

Water-soluble nitrogen can be absorbed by turfgrass roots as long
as there is sufficient moisture in the soil. Such high solubility has
both advantages and disadvantages. Turfgrass responds rapidly after
their application but the response is short term. This is because much
of the nitrogen is immediately taken up by plants, leached below the
root zone, or lost to the atmosphere as a gas. These forms of nitrogen
are less expensive than more complex, insoluble carriers. Fast-release
nitrogen is not greatly affected by soil temperature. However, it has a
high burn potential and can injure turfgrass if applied incorrectly
(Figure 10-6).

Some of the disadvantages associated with water-soluble carriers
pose special problems for the turf manager. Turfgrass is one of the few
crops that has fertilizer applied directly onto its foliage. This
increases the likelihood of foliar burn. The short-term plant response
characteristic of these carriers means that frequent fertilization may
be required. Another problem is the inefficiency of the water-soluble
forms. Nitrogen is wasted because the turfgrass plants are able to take
up more nitrogen than they need, and leaching and gaseous losses may be
significant. This can be a serious problem if the nitrates leach down
into the groundwater.

Slowly available nitrogen carriers were developed to solve the
problems associated with the quickly available forms. They are also
referred to as slow-release or controlled-release. A certain percentage
of the nitrogen in these carriers is not immediately soluble in water
and therefore not initially available for plant use. The result is a
lower burn potential, a long-term plant response, and greater efficiency
(Figure 10-7). A steadier release pattern reduces the likelihood of
plants absorbing more nitrogen than they need and decreases leaching
losses.

Slowly available nitrogen carriers are more expensive than soluble
forms because the manufacturing process is more costly.

[FIGURE 10-6 OMITTED]

Ureaformaldehyde (UF), sulfur-coated urea (SCU), polymer-coated
urea (PCU), and isobutylidenediurea (IBDU) are examples of slowly
available nitrogen carriers. All are produced by chemical processes that
result in a certain percentage of the nitrogen in urea becoming
temporarily unavailable for plant use.

Urea formaldehyde is synthesized by combining urea and
formaldehyde. When a ureaformaldehyde (U:F) ratio of 1.3:1.0 is used,
the resulting product has approximately 67 percent slowly soluble
nitrogen. The other 33 percent is called cold water-soluble nitrogen
(CWSN). It is composed of unreacted urea and low molecular weight,
short-chain methylene ureas that immediately provide nitrogen to
turfgrasses. The rest of the nitrogen does not become available until
the larger molecules are broken down into smaller units by soil
microorganisms, freeing the urea. The cold water-insoluble nitrogen
(CWIN) that is soluble in hot water is intermediate or moderately slow
release, and the fraction that is insoluable in hot-water (HWIN) is very
slowly soluble.

The intermediate chain-length material is sometimes referred to as
methylene urea. The longer the chain, the slower the release of the
nitrogen.

One problem with UF is its dependence on higher temperatures for
adequate nitrogen solubility. Microbial degradation of the slowly
soluble forms is minimal at cool soil temperatures. Consequently,
nitrogen availability is significantly reduced, and enough nitrogen may
not be supplied by this carrier at certain times of the year. The
nitrogen activity index (AI) is a measure of relative solubility. It is
the percentage of CWIN that is soluble in hot (212[degrees]F,
100[degrees]C) water. The higher the AI, the more rapidly the slowly
available nitrogen becomes soluble. A UF material should have an AI of
at least 40 percent to ensure that sufficient quantities of nitrogen
will be supplied to turfgrass during the year following application.

The solubility of a UF fertilizer is controlled by the UF ratio. A
1.9:1.0 ratio product results in shorter polymer chains, has 67 percent
CWSN, and provides a much greater quantity of soluble nitrogen. This and
similar ratios are popular where cooler soil temperatures cause reduced
levels of microbial activity.

[FIGURE 10-7 OMITTED]

Sulfur-coated urea is simply urea granules that have been covered
with sulfur. The urea is water soluble, but the sulfur coat produces an
insoluble barrier. The granule is also coated with a thin layer of wax
to seal any cracks or defects in the sulfur coat. Eventually the coating
is burst open because of the diffusion of water into the granule through
micropores, cracks, and imperfections, and the nitrogen is released. The
wax is degraded by microorganisms.

The coating thickness varies among particles. Those that have a
thin or imperfect coat will release first. Approximately 30 percent of
the nitrogen in most SCU products is quickly available. By blending
particles with thin, medium, and thick coats, manufacturers can make
products that release nitrogen steadily for ten to fifteen weeks.

Sulfur-coated urea is popular because it is the least expensive of
the slowly available nitrogen sources. However, problems can result if
the fertilizer is damaged during handling. If the sulfur coats are
cracked, the particles are no longer slow release.

A method of producing a more precise form of slowly available
nitrogen is to surround urea with a polymer, plastic, or resin coating.
These ultrathin coats are tough and durable. Moisture is absorbed by the
coating and dissolves the urea; then the solution diffuses out into the
soil. Most of these products are relatively new and are often called
polymer-coated ureas (PCUs). They have a very uniform release rate, the
length of which depends primarily on the thickness of the coating
(Figure 10-8).

A PCU is more expensive than an SCU because coating urea with a
polymer is more expensive than coating it with sulfur. Another technique
is to apply a thinner than usual coating of sulfur to urea, then
covering it with a polymer coat thinner than that used on a normal PCU.
The resulting product is cheaper than a PCU but has a more precise
release pattern than an SCU.

IBDU is similar to UF but is less affected by soil temperature. The
nitrogen dissolves in water slowly, but does not depend on microbial
decomposition. Particle size has the major effect on solubility. Smaller
particles dissolve more readily and release soluble nitrogen faster than
larger particles. A blend of different-sized particles results in a
fertilizer that releases nitrogen relatively uniformly for three or four
months. However, low or high soil pH can impede nitrogen release. IBDU
is popular for late-season feeding because it can release nitrogen at
colder soil temperatures like the soluble sources but without leaching
problems, and will not cause a spurt of topgrowth if a few warm days
occur.

[FIGURE 10-8 OMITTED]

Organic matter releases nitrogen gradually because the nutrient is
tied up in complex molecules. The nitrogen becomes available after
microorganisms break down the complex molecules into simpler forms.

Milorganite is a natural organic fertilizer produced from sewage
sludge by the Milwaukee Sewage Commission. Other products are derived
from dried blood, bone and seed meal, fish scraps, poultry feathers and
manure, and compost. Ringer, Sustane, and Nature Safe are examples of
natural fertilizers (Figure 10-9). Besides being slowly available
nitrogen sources, natural organic fertilizers also provide the other
essential nutrients and have been shown to suppress turf diseases. They
have a very low burn potential but are more expensive nitrogen sources
than other types of fertilizers (Figure 10-10). This is because the
natural organic materials contain small amounts of nitrogen and often
have to be shipped long distances. Sometimes urea is added to them to
increase the percentage of nitrogen.

Natural organic fertilizers are viewed positively by the public
because they are recycled waste and are considered to be
"environmentally sound" products.

Fast-release and slow-release nitrogen carriers have advantages and
disadvantages. Many companies that manufacture turfgrass fertilizers mix
soluble and insoluble carriers to ensure both a rapid and a long-term
response (Figure 10-11).

[FIGURE 10-9 OMITTED]

Potassium

Potassium has numerous functions in a plant. It counteracts many of
the negative effects of nitrogen such as decreased plant tolerance to
cold, heat, drought, and diseases. If turfgrass is supplied with
adequate amounts of potassium, the ability of the plants to tolerate
stress is increased.

Muriate of potash (potassium chloride) is the carrier commonly
added to a fertilizer. It has a high burn potential (Figure 10-12).
Potassium sulfate has a lower burn potential and releases potassium more
gradually than muriate of potash. Though more expensive, potassium
sulfate is a better choice for quality turf areas. Slow-release,
polymer-coated potassium fertilizers are also available.

Potassium is susceptible to leaching. The problem, however, is more
severe with nitrogen. Plants will absorb significantly greater amounts
of potassium than they require. This is known as "luxury
consumption." Large quantities of potassium may be removed if
clippings are collected. This is more of a problem with muriate of
potash than it is with potassium sulfate or polymer-coated sources. Soil
tests can be used to estimate potassium needs. Turf fertilizers with a
2:1 N:[K.sub.2]O ratio are often recommended unless soil test results
indicate that less or more potassium is needed. Some turf managers use
1:1 ratios in an attempt to increase the winter hardiness or drought
tolerance of their grass. Potassium is very important in regulating
water absorption and retention in a plant.

Phosphorus

Phosphorus has many important roles in a plant. A prominent
characteristic is its ability to promote rooting. Adequate levels of
phosphorus are crucial at the time of establishment. The nutrient should
be incorporated into the soil before planting, and then, after planting,
the new seedlings or sod should be top-dressed with phosphorus
fertilizer. All application should be based on soil test results.

The major problem with phosphorus is its "fixation" in
the soil. At a soil pH below 6.0 and above 7.0 phosphorus becomes tied
up in unavailable, insoluble forms. Maintaining the correct soil pH
increases phosphorus availability. Super-phosphate was for many years
the primary phosphorus carrier. Today, ammonium phosphates are used in
most fertilizers (Table 10-1).

Phosphorus has been identified as a potential water pollutant. If
large enough quantities accumulate in lakes and ponds, algal blooms and
other water-quality problems can occur (Figure 10-13). Turfgrass
fertilizers are occasionally the source of some of the phosphorus that
is found in bodies of water. The fertilizer runs off into the lake or
pond because it is applied too close to the water or on a slope near the
water. Some may be accidentally spread on an adjacent driveway or road
where it can wash into a storm drain that empties into a body of water.
If some of the phosphorus lands on bare soil, it will move with the soil
if erosion occurs.

It is important that phosphorus be applied only when soil test
results show a need. Many turf areas have adequate phosphorus levels
because it is not readily lost once it is in the soil. When phosphorus
is used, it should be watered in after the application. However, too
much irrigation will result in runoff. Fertilizer should not be applied
if a heavy rain is predicted.

Some states are considering regulating the use of
phosphorus-containing fertilizers. Some municipalities already have
regulations in place.

[FIGURE 10-13 OMITTED]

Fertilizer Programs

Fertilizer application rates and the number of applications are
determined by many factors, such as the desired level of quality,
weather conditions, the length of the growing season, soil texture, the
amount of irrigation provided, and whether clippings are removed.
Environmental conditions affect the fertilizer program. Shaded turf,
because it grows more slowly, is usually fertilized less than grass
growing in the full sun. Turf use influences fertility requirements. An
athletic field often needs more fertilizer than a lawn because sports
turf has to recover from wear injury.

The species and cultivars that compose the turf have a major effect
on fertilizer programs. Creeping bentgrass and improved bermudagrass are
considered heavy feeders because they grow vigorously and need abundant
amounts of nutrients to support this growth. Grasses that have a slow
growth rate such as the fine fescues, centipedegrass, and carpetgrass
need significantly less fertilization. Soil test results help the turf
manager to develop the program.

Application dates also depend on many of the same variables listed
earlier. Weather conditions have the greatest influence on timing.
Fertilization should occur at the beginning of or during periods when
temperature and moisture conditions favor active turfgrass growth. The
grass needs the nutrients when it is growing vigorously. Fertilization
should be avoided at times when environmental and disease stress occurs.
For example, a midsummer fertilizer application can be detrimental to
cool season turf because it results in decreased heat, drought, and
disease tolerance.

The most important time to fertilize cool season grasses is in late
summer or early fall. A late fall fertilization in November is also
beneficial. The fertilizer is usually applied when the rate of shoot
growth has slowed significantly but the grass is still green. It
promotes root growth and earlier spring greenup. A third application in
the spring is recommended as well for better quality turf. Often a lower
nitrogen rate is used at this time.

The most important time to fertilize warm season grasses is in late
spring. A second application in the summer is recommended. Early spring
and late summer fertilization may also be necessary (Table 10-2).

The most common fertilizer application rate is 1/2 to 1 pound of
nitrogen per 1,000 [ft.sup.2] (1.1-2.2 kilograms per 93 [m.sup.2]). Golf
course putting greens are an exception. They usually receive frequent,
light rates. Turf requires fewer applications when slow-release nitrogen
sources are used rather than fast-release products. Because of less
nutrient storage capacity and greater leaching potential, sandy soils
are fertilized at lower rates and more frequently than loam and clay
soils.

The turf manager should use soil test results and Cooperative
Extension Service recommendations as the basis for a fertility program.
Nitrogen, phosphorus, and potassium receive the most attention, but
other essential elements should not be overlooked. Iron deficiencies
occur, especially on soils that are alkaline, sandy, or high in organic
matter. Sometimes the application of iron causes grass to become a
darker green color. Nitrogen also improves color. However, iron will not
stimulate the rapid shoot growth that nitrogen will. Consequently, iron
can be used to give turf a better color without increasing its
maintenance requirements or causing the grass to be less tolerant of
environmental stress. Liquid foliar applications often work best, but
results are not long-lasting due to the removal of iron on the leaf
tissue when the grass is cut.

Magnesium and calcium may be deficient on very sandy soils. Sand
golf greens often require the addition of other nutrients besides
nitrogen, phosphorus, and potassium. Relatively specific fertilizer
programs for golf courses, lawns, athletic fields, and other turf areas
are discussed in Chapters 20, 21, and 22.

Application Methods

Granular Fertilizers

The majority of the fertilizer used on turfgrass is in a dry or
granular form. It is distributed with a drop, rotary, or pendulum-type
spreader. The drop, or gravity-type, spreader has a series of openings
at the bottom of the hopper through which granular fertilizer drops a
few inches to the ground directly beneath (Figure 10-14). The rate of
application can be changed by adjusting the size of the openings. Drop
spreaders provide a very precise, uniform distribution pattern.

The width of homeowner-type drop spreaders is usually 2 feet (0.6
meter), but wider models are available. Drop spreaders are normally
preferred for the application of fine or very light particles such as
ground limestone, or granular pesticides that must stick to the foliage.
Too much overlapping or misses between application swaths can result in
streaking because of uneven nitrogen distribution.

Rotary spreaders are also called centrifugal, broadcast, or cyclone
spreaders. Most have a plate, called an impeller, which is attached
beneath the hopper and spins as the spreader wheels turn. When
fertilizer drops through the adjustable openings at the bottom of the
hopper, it falls onto the rotating impeller and is thrown away from the
spreader in a semicircular pattern (Figure 10-15).

[FIGURE 10-14 OMITTED]

Application is faster with a rotary spreader because it broadcasts
granular materials over a wider area than the drop type. The spreading
width normally ranges from 6 feet (1.8 meters) for small spreaders to 60
feet (18.3 meters) for very large ones. Streaking is less likely with
rotaries because the swaths are overlapped and the edge of the
distribution pattern is not as sharp as that produced by a drop
spreader.

A rotary spreader does not provide as accurate and uniform an
application as a drop spreader, but the distribution can be quite
satisfactory if the proper overlap is used. Spreading mixed materials of
different sizes is a problem because larger, heavier granules are thrown
farther than smaller, lighter particles. Foliar-applied granular
pesticides are not usually spread with a rotary spreader because of
unsatisfactory distribution. Ground limestone will often drift when
applied with a rotary spreader. The speed at which the spreader is
pushed or driven has a major impact on application rate.

Pendulum-type spreaders have a spout that moves from side to side.
They are pulled by a tractor or turf vehicle, have a large hopper
capacity, and can throw dry materials a great distance when the spout
moves rapidly.

Spreaders should be thoroughly cleaned after use. They must be
accurately calibrated (openings set at the proper size) to ensure that
the correct amount of material is applied. Spreader care and calibration
are discussed in Appendix C.

Liquid Fertilizers

The application of fertilizer in a liquid form has become popular
with many lawn care companies and golf course superintendents. The
fertilizer is sprayed on the turf and is often mixed with pesticides. On
golf courses, at certain times, such low rates of nutrients are applied
to greens that it would be impossible to apply them uniformly with a
spreader. Liquid application is usually less expensive than granular
applications, though the initial cost of the sprayer equipment is quite
high compared to the cost of a spreader. Generally 3 to 5 gallons (11.4
to 19.0 liters) of the fertilizer-water mixture is applied per 1,000
[ft.sup.2] to ensure that the fertilizer is washed into the root zone.
Urea is the most widely used fertilizer material because it is soluble
in water. Unfortunately, urea has a high burn potential and releases
most of its nitrogen in a few weeks, so ideally it should be sprayed
frequently at light rates. Products are now available that have a lower
burn potential and somewhat longer-lasting effects.

[FIGURE 10-15 OMITTED]

The application of small amounts of nutrients in low spray volumes
(0.5 gallon per 1,000 [ft.sup.2]) directly to the foliage is called
foliar feeding. Some of the fertilizer is absorbed by the turfgrass
leaves. Foliar feeding is used to supply micronutrients such as iron and
nitrogen.

Fertigation is the application of nutrients through the irrigation
system (Figure 10-16). Minute amounts of fertilizer are regularly
metered into the irrigation lines and distributed along with the
irrigation water through the sprinkler heads. The irrigation system must
be capable of distributing water very uniformly. The advantages of
fertigation include a more efficient plant use of nutrients, a steadier
growth rate, and a savings on labor costs. Fertigation occurs on some
golf courses, but is not yet widely used.

Its use will increase because on many new golf courses the
irrigation systems are designed to accommodate fertilizer injection
systems. Fertigation is very popular during the grow-in period on
recently constructed golf courses because there is no need to drive
tractors pulling fertilizer spreaders over the easily-injured young
grass.

[FIGURE 10-16A OMITTED]

[FIGURE 10-16B OMITTED]

Fertilizer Burn

Fertilizer or foliar burn can be a serious problem if fertilizers
are applied improperly. Soluble, fast-release nutrient sources in both
liquid and granular forms should be watered in following application.
Irrigation moves the fertilizer off the foliage into the soil and
prevents burning of the leaves. It does not occur after foliar feeding
because very low fertilizer rates are applied. The foliage should be dry
when granular fertilizers are applied (Figure 10-17). Fast-release
nitrogen generally should not be applied at rates higher than 0.5 pound
of nitrogen per 1,000 [ft.sup.2].

If an overapplication of fertilizer occurs, heavy irrigation is
recommended. If a spill of granular fertilizer occurs, as much
fertilizer as possible should be picked up before irrigating.

[FIGURE 10-17 OMITTED]

SELF-EVALUATION

1. The two nutrients generally supplied by liming materials are --
and --.

2. Nitrogen losses on a sandy soil can be severe because of --.

3. The ratio of a 30-15-15 fertilizer is --.

4. The second number in a fertilizer grade represents the
percentage of -- in the bag.